Recently, multifunctional and high-end portable electronic devices have been developed according to the development of multimedia devices and the convergence of electronic devices. These portable devices have a haptic piezoelectric element for implementing a sense of touch by a vibration force among various functions and use the haptic piezoelectric element as a means of providing a three-dimensional touch to users when driving various applications such as games or text input.
Currently, mobile devices including smartphones mostly execute text input and applications using a touch screen. In the past, a method of implementing a haptic function by driving a vibration motor embedded in a mobile device with a driving voltage generated by a current applied when touching a touch screen was mainly used, but the touch screen has been rapidly replaced by the piezoelectric element in the recent high-end mobile devices since the touch screen has a low reaction speed compared to low cost.
The piezoelectric element is operated by the electric field formed between two electrodes, that is, an anode and a cathode by applying a voltage to a piezoelectric material, causes the deformation of structure by the dipole generated inside the piezoelectric material through the movement of the electric field, and generates vibration by the mechanical displacement in the longitudinal or cross-sectional direction through the structural deformation.
The piezoelectric element can realize an immediate haptic function since the reaction speed of the piezoelectric element is several times faster than the conventional vibration motor in converting an electrical signal to mechanical displacement.
However, since a desired type of vibration force is implemented when various types of module structures are accompanied to adjust the mechanical displacement of the piezoelectric element and the piezoelectric material constituting the piezoelectric element requires a high operating voltage, it is difficult to implement a high vibration force under a limited operating voltage of the mobile device.
Therefore, currently, there exists a need for developing a piezoelectric element for implementing a high vibration force while reducing the overall operating voltage.                Patent Document 1: Japanese Patent Laid-Open Publication No. 2013-016548        